$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid5 sdd1[5] sde1[4] sdc1[2] sdb1[1] nvme0n1p1[0](J)
      20508171264 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UU_U]
      [>....................]  recovery =  0.0% (5811228/6836057088) finish=626.8min speed=181600K/sec